(Science: botany) A trifoliate plant used as a national emblem by the irish. The legend is that St. Patrick once plucked a leaf of it for use in illustrating the doctrine of the trinity.
The original plant was probably a kind of wood sorrel (oxalis Acetocella); but now the name is given to the white clover (trifolium repens), and the black medic (Medicago lupulina).
Origin: L. Seamrog, seamar, trefoil, white clover, white honeysuckle; akin to Gael. Seamrag.